rcu: Add sparse check to rcu_assign_pointer()

The rcu_assign_pointer() function currently doesn't do any sparse checking
on the assigned-to pointer.  So its possible that a pointer that is
not __rcu annotated is assigned with rcu_assign_pointer without sparse
complaints.  Because rcu_dereference() already does such checking,
this commit makes rcu_assign_pointer() to do the same. The extra
error could be helpful in cases where an RCU pointer is assigned with
rcu_assign_pointer() but not annotated with __rcu.

This doesn't generate any code in the normal case because __CHECKER__ is
defined only in the context of sparse.

This commit also renames rcu_dereference_sparse() to rcu_check_parse()
since the checking now happens not only during derereferencing but also
during assignment.

Test: Introduced an rcu_assign_pointer in code and checked the output of
sparse with and without this change. The change correctly causes sparse
to throw an error.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 6f8f047c406842977e3a9c6f455f593fecf145b7..4a2cce4d4bd94f2e4f795b1012fabf0f6da9e2bb 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -309,16 +309,16 @@ static inline void rcu_preempt_sleep_check(void) { }
  */
 
 #ifdef __CHECKER__
-#define rcu_dereference_sparse(p, space) \
+#define rcu_check_sparse(p, space) \
        ((void)(((typeof(*p) space *)p) == p))
 #else /* #ifdef __CHECKER__ */
-#define rcu_dereference_sparse(p, space)
+#define rcu_check_sparse(p, space)
 #endif /* #else #ifdef __CHECKER__ */
 
 #define __rcu_access_pointer(p, space) \
 ({ \
        typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
-       rcu_dereference_sparse(p, space); \
+       rcu_check_sparse(p, space); \
        ((typeof(*p) __force __kernel *)(_________p1)); \
 })
 #define __rcu_dereference_check(p, c, space) \
@@ -326,13 +326,13 @@ static inline void rcu_preempt_sleep_check(void) { }
        /* Dependency order vs. p above. */ \
        typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
        RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
-       rcu_dereference_sparse(p, space); \
+       rcu_check_sparse(p, space); \
        ((typeof(*p) __force __kernel *)(________p1)); \
 })
 #define __rcu_dereference_protected(p, c, space) \
 ({ \
        RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
-       rcu_dereference_sparse(p, space); \
+       rcu_check_sparse(p, space); \
        ((typeof(*p) __force __kernel *)(p)); \
 })
 #define rcu_dereference_raw(p) \
@@ -382,6 +382,7 @@ static inline void rcu_preempt_sleep_check(void) { }
 #define rcu_assign_pointer(p, v)                                             \
 ({                                                                           \
        uintptr_t _r_a_p__v = (uintptr_t)(v);                                 \
+       rcu_check_sparse(p, __rcu);                                   \
                                                                              \
        if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL)        \
                WRITE_ONCE((p), (typeof(p))(_r_a_p__v));                      \
@@ -785,7 +786,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  */
 #define RCU_INIT_POINTER(p, v) \
        do { \
-               rcu_dereference_sparse(p, __rcu); \
+               rcu_check_sparse(p, __rcu); \
                WRITE_ONCE(p, RCU_INITIALIZER(v)); \
        } while (0)